The present invention generally relates to a circuit element, and more particularly, to a non-reciprocal circuit element such as a circulator or isolator to be employed as a high frequency part for a microwave band region, which is especially so arranged to decrease cost through reduction of the number of parts and man-hours required for assembly, with simultaneous achievement of compact size and light weight.
Generally, a circulator or isolator has such a function that it has almost no attenuation in the direction of transmission of a signal, with an increasing attenuation of the signal in a direction opposite thereto, and is employed, for example, in a transmission circuit of a mobile communication apparatus such as a portable telephone, automobile telephone or the like.
For such an isolator, there has conventionally been available an arrangement as shown in FIG. 15.
In FIG. 15, the known isolator 40 generally includes a magnetic material metallic case 41, a ferrite assembly 44 constituted by a pair of ferrite members 43 confronting a plurality of central conductors 42, and disposed within the metallic case 41, with said ferrite assembly 44 being located in central holes 45a of a pair of dielectric substrates 45 which have, on the inner surface thereof, a capacitor electrode for a matching circuit, and a pair of permanent magnets 47 held in contact with ground electrodes formed on the outer surface of each of said dielectric substrates 45 respectively through shield plates 46. More specifically, the above ferrite assembly 44 is composed of three sets of network central conductors 42 made for example, of copper plates, and piled up one upon another in an electrically insulated state separated by insulative sheets, crossing or intersecting each other at 120.degree. angles so as to be held between the two ferrite members 43. To external lead-out portion 42a at each end of each of the central conductors 42, there are connected one end of each of input and output terminal strips 48 embedded in a rectangular frame-like block 49 of a resin material disposed along an inner peripheral edge of the case 41, while the other end of said terminal strips 48 project outwardly from an opening 41a formed in said case 41.
When an isolator or circulator is to be employed, e.g. in a portable telephone, a reduction in the cost of its parts is required from the viewpoint of its end use, with a simultaneous demand for compact size and light weight.
However, the conventional isolator as referred to above has such a disadvantage that it can not fully meet the requirement of cost reduction due to its construction, and there are limitations on the compact size and weight reduction that are available.
More specifically, assembling of the conventional ferrite assembly involves a complicated process in which the insulative sheets are inserted between the respective central conductors, while said central conductors are alternately crossed over each other, and moreover, such assembly must be inserted into the case through proper positioning. Accordingly, the number of parts and man-hours required for assembling are undesirably increased, with an increase of cost to that extent.
Additionally, due to the employment of the metallic case, it is necessary to make the case rather larger so as to provide a space between the case and circuit elements for avoiding short-circuits resulting from contact of the case with the respective circuit elements, thus also resulting in a larger size, while the weight reduction is obstructed due to employment of the metallic material for the case.